Circuit device and oscillator

Abstract

Provided is a circuit device including: an oscillation circuit configured to generate an oscillation signal; a waveform shaping circuit configured to shape the oscillation signal into a clock signal having a rectangular wave; a low-pass filter configured to smooth the clock signal and generate a detection voltage corresponding to a duty of the clock signal; and a differential amplifier configured to output a bias voltage based on a difference between the detection voltage and a reference voltage to an input node of the waveform shaping circuit, in which a unity gain frequency of the differential amplifier is lower than a cutoff frequency of the low-pass filter.

What is claimed is: 
     
         1 . A circuit device comprising:
 an oscillation circuit configured to generate an oscillation signal;   a waveform shaping circuit configured to receive the oscillation signal to shape the oscillation signal into a clock signal having a rectangular wave;   a low-pass filter configured to receive the clock signal from the waveform shaping circuit to smooth the clock signal and generate a detection voltage corresponding to a duty of the clock signal; and   a differential amplifier configured to receive the detection voltage from the low-pass filter and output a bias voltage based on a difference between the detection voltage and a reference voltage to an input node of the waveform shaping circuit, wherein   a unity gain frequency of the differential amplifier is lower than a cutoff frequency of the low-pass filter.   
     
     
         2 . The circuit device according to  claim 1 , wherein
 the unity gain frequency of the differential amplifier is equal to or lower than half of the cutoff frequency of the low-pass filter.   
     
     
         3 . The circuit device according to  claim 1 , wherein
 the unity gain frequency of the differential amplifier is equal to or lower than 1/10 of the cutoff frequency of the low-pass filter.   
     
     
         4 . The circuit device according to  claim 1 , further comprising:
 a resistance voltage-dividing circuit configured to divide a regulator voltage and generate the reference voltage.   
     
     
         5 . The circuit device according to  claim 4 , wherein
 the resistance voltage-dividing circuit includes a plurality of resistance elements coupled in series and a switch circuit configured to select one of nodes between the plurality of resistance elements and output the reference voltage.   
     
     
         6 . The circuit device according to  claim 1 , wherein
 the waveform shaping circuit includes a first inverter to which the oscillation signal is input, and a second inverter configured to invert an output signal of the first inverter to generate the clock signal, and   the reference voltage is generated by smoothing the output signal of the first inverter.   
     
     
         7 . The circuit device according to  claim 1 , wherein
 no low-pass filter is provided between the oscillation circuit and the waveform shaping circuit.   
     
     
         8 . An oscillator comprising:
 the circuit device according to  claim 1 ; and   a resonator, wherein   the oscillation circuit causes the resonator to oscillate to generate the oscillation signal.